1. Field of the Invention
The present invention relates to a glass antenna device for an automobile having a high receiving sensitivity and flatness of receiving sensitivity within a desired broadcast frequency band region.
2. Discussion of the Background
In a glass antenna for receiving signals in an AM broadcast frequency band region (hereinbelow, referred to as an AM band) and an FM broadcast frequency band region (hereinbelow, referred to as an FM band), it has been known to insert a pre-amplifier at a desired position in a feeder line between a feeding terminal for an antenna conductor and a receiver to compensate an insufficient receiving sensitivity of the antenna. However, there occurred waveform distortion and cross modulation in a strong electric field due to the presence of the pre-amplifier to thereby amplify noises.
The conventional technique had problems as follows. Productivity decreased since it was necessary to dispose another pre-amplifier in addition to that for the receiver. Further, the pre-amplifier to be disposed near the glass antenna restricted the condition of designing an automobile, e.g. in obtaining a space for the pre-amplifier. Accordingly, it has been expected to develop a glass antenna device for an automobile having a high receiving sensitivity and non-directivity, and capable of suppressing noises, without the necessity of the pre-amplifier.
In order to eliminate the above-mentioned disadvantage, a glass antenna device disclosed in U.S. Pat. No. 5,083,134 is proposed. The publication discloses an antenna device for an automobile comprising an electric heating type defogger having heater strips and a bus bar for feeding a current to the heater strips and antenna conductors arranged to form a pattern wherein the defogger and the antenna conductors are formed on a glass sheet to be fitted to a rear window opening of an automobile, and wherein the defogger and the antenna conductors are disposed with a predetermined small space in a capacitive coupling relation so that an intermediate or a high frequency current is caused to flow but a direct current is not caused to flow between them, and a reactance circuit is connected between the bus bar and a d.c. power source for the defogger, whereby there is an anti-resonance point in a desired broadcast frequency band region, which is caused by impedance composed mainly of capacitance which is produced in correlation among the antenna conductors, the defogger and the body of automobile and the impedance of the reactance circuit, and there is a resonance point in the desired broadcast frequency band region, which is caused by the impedance of a predetermined circuit connected between a feeding terminal for the antenna conductors and a receiver, the input impedance of the receiver, and the impedance of the antenna conductor side viewed from the predetermined circuit.
In the proposed glass antenna device, however, it was difficult to make the receiving sensitivity flat in its entirety of the broadcast frequency band region because both the resonance point and the anti-resonance point exist in the broadcast frequency band region. If the construction of circuit was modified to reduce appropriately the value of Q (quality factor) so that the receiving sensitivity was made flat, the receiving sensitivity became worse.
Further, the existence of the anti-resonance point in the desired broadcast frequency band region decreased the S/N ratio by about several decibels (dB) in comparison with the existence of the anti-resonance point out of the desired broadcast frequency band region because noises are apt to occur near the anti-resonance point. However, the reason is not always theorically clear.
It is an object of the present invention to provide a glass antenna device for an automobile providing the characteristics of high gain, low noise level, non-waveform-distortion, non-cross-modulation and non-directivity, and excellent flatness of receiving sensitivity, without disposing a pre-amplifier.
In an aspect of the present invention, there is provided a glass antenna device for an automobile comprising:
a glass sheet fitted to a rear window opening of an automobile; PA1 an electric heating type defogger having heater strips and bus bars for feeding a current to the heater strips; PA1 antenna conductors arranged to have a pattern and spaced with a predetermined distance apart from the defogger in a capacitive coupling relation so that a direct current is not caused to flow but an intermediate or a high frequency current is caused to flow between the antenna conductors and the defogger, PA1 the defogger and the antenna conductors being formed on the glass sheet; and PA1 a reactance circuit connected between the bus bars and a d.c. power source for the defogger, PA1 the glass antenna device being characterized in that: PA1 there is an anti-resonance point caused by impedance composed mainly of capacitance which is produced in correlation among the antenna conductors, the defogger and the body of automobile and the impedance of the reactance circuit, the anti-resonance point being out of a predetermined receiving frequency band region or a predetermined broadcast frequency band region, and PA1 there is a resonance point between the frequency of 1.5 times of f.sub.H and f.sub.L, where f.sub.H is the highest frequency in the predetermined receiving frequency band region or the predetermined broadcast frequency band region and f.sub.L is the lowest frequency of the same, which is caused by the impedance of a predetermined circuit connected between a power feeding terminal for the antenna conductors and a receiver; the input impedance of the receiver and the impedance of the antenna conductor side viewed from the predetermined circuit. PA1 a glass sheet fitted to a rear window opening of an automobile; PA1 an electric heating type defogger having heater strips and bus bars for feeding a current to the heater strips; PA1 antenna conductors arranged to have a pattern and spaced with a predetermined distance apart from the defogger in a capacitive coupling relation so that a direct current is not caused to flow but an intermediate or a high frequency current is caused to flow between the antenna conductors and the defogger, PA1 the defogger and the antenna conductors being formed on the glass sheet; and PA1 a reactance circuit connected between the bus bars and a d.c. power source for the defogger, PA1 the glass antenna device being characterized in that: PA1 there is an anti-resonance point between (2/3).multidot.(f.sub.L.sup.2 /f.sub.H) and f.sub.L where f.sub.H is the highest frequency in a predetermined receiving frequency band region or a predetermined broadcast frequency band region and f.sub.L is the lowest frequency of the same, wherein the anti-resonance point is caused by impedance composed mainly of capacitance which is produced in correlation among the antenna conductors, the defogger and the body of automobile and the impedance of the reactance circuit, and is out of the predetermined receiving frequency band region or the predetermined broadcast frequency band region, and PA1 there is a resonance point between f.sub.L +(f.sub.H -f.sub.L).multidot.(0.3) and (1.2).multidot.f.sub.H wherein the resonance point is caused by the impedance of a predetermined circuit connected between a power feeding terminal for the antenna conductors and a receiver; the input impedance of the receiver and the impedance of the antenna conductor side viewed from the predetermined circuit. PA1 a glass sheet fitted to a rear window opening of an automobile; PA1 an electric heating type defogger having heater strips and bus bars for feeding a current to the heater strips; PA1 antenna conductors arranged to have a pattern and spaced with a predetermined distance apart from the defogger in a capacitive coupling relation so that a direct current is not caused to flow but an intermediate or a high frequency current is caused to flow between the antenna conductors and the defogger, PA1 the defogger and the antenna conductors being formed on the glass sheet; and PA1 a reactance circuit connected between the bus bars and a d.c. power source for the defogger, PA1 the glass antenna device being characterized in that: PA1 there is an anti-resonance point between f.sub.arL +(f.sub.L -f.sub.arL).multidot.(0.25) and (0.9).multidot.f.sub.L where f.sub.H is the highest frequency in a predetermined receiving frequency band region or a predetermined broadcast frequency band region, f.sub.L is the lowest frequency of the same, and (2/3).multidot.(f.sub.L.sup.2 /f.sub.H)=f.sub.arL and wherein the anti-resonance point is caused by impedance composed mainly of capacitance which is produced in correlation among the antenna conductors, the defogger and the body of automobile and the impedance of the reactance circuit, the anti-resonance point being out of the predetermined receiving frequency band region or the predetermined broadcast frequency band region, and PA1 there is a resonance point between f.sub.L +(f.sub.H -f.sub.L).multidot.(0.6) and f.sub.H wherein the resonance point is caused by the impedance of a predetermined circuit connected between a power feeding terminal for the antenna conductors and a receiver; the input impedance of the receiver and the impedance of the antenna conductor side viewed from the predetermined circuit.
In another aspect of the present invention, there is provided the above-mentioned glass antenna device wherein the anti-resonance point is caused by impedance composed mainly of capacitance which is produced in correlation among the antenna conductors, the defogger and the body of automobile and the impedance of the reactance circuit in a lower frequency area out of the predetermined receiving frequency band region or the predetermined frequency band region.
In another aspect of the present invention, there is provided a glass antenna device for an automobile comprising:
In another aspect of the present invention, there is provided a glass antenna device for an automobile comprising: